A car navigation system aids a vehicle operator to navigate by allowing the vehicle operator to designate a destination on a map stored in a storage unit such as HDD and DVD-ROM, determining an optimum route to the designated destination and identifying the current position of the vehicle according to the position information obtained from GPS satellites. A destination can be designated in a number of different ways such as addresses, spot names, telephone numbers, ZIP codes and so on.
The address is considered to be highly reliable and convenient in designating a destination. An address is given as a combination of data of several hierarchy levels, and can be narrowed down to progressively lower hierarchy levels. For instance, the topmost hierarchy level may consist of “state”, and the second hierarchy level “city”, the third hierarchy level “street”, and the fourth hierarchy level “house number”. Typically, a car navigation system is equipped with a user interface in such forms as a touch screen showing an alphanumeric keypad and a remote control combined with a video display to enable the vehicle operator to enter a desired command.
Japanese patent laid open publication No. 2001-41762 discloses an arrangement in which a number of candidates each in the form of a string of characters are displayed for each hierarchy level so that the vehicle operator may select a candidate in each hierarchy level from the topmost one to the lowermost one. Japanese patent laid open publication No. 2004-127049 discloses an arrangement in which an alphanumeric keypad is displayed on a monitor so that the vehicle operator may enter a string of characters for designating a destination.
However, the conventional arrangements for designating and retrieving the address of a destination were not entirely satisfactory in regards to efficiency and convenience. According to the arrangement disclosed in Japanese patent laid open publication No. 2001-41762, the 50 states (the first hierarchy) are displayed, and upon selecting one of the states, a large number of cities belonging to the selected state (second hierarchy) are displayed. Therefore, the vehicle occupant has to scroll the display until a desired city is shown, and it therefore requires a long time for the vehicle operator to be able to select the desired city. According to the arrangement disclosed in Japanese patent laid open publication No. 2004-127049, the vehicle operator has to enter a string of characters from a keypad displayed on the monitor, and may be required to enter a large number of characters before obtaining the name of the desired city. Also, in either case, if the vehicle operator knows the name of the city but does not know the name of the state, the vehicle operator is not able to move on from the first hierarchy to the second, and is unable to designate the destination at all.